I think that this behavior is in keeping with The SUS standard. Quoting from the
SUS 3 standard:
The system shall always zero-fill any partial page at the end of an object.
Further, the system shall never write out any modified portions of the last page
of an object which are beyond its end. [MPR] [Option Start] References within
the address range starting at pa and continuing for len bytes to whole pages
following the end of an object shall result in delivery of a SIGBUS signal.
[Option End]
This seems to imply that one can map past the end of the end of the object. And
in fact, linux devlivers a SIGBUS in thish case.

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